Geographic Range

Habitat

Pollicipes polymerus is found on rocky cliffs in the splash zone. They inhabit very high-energy environments because they can withstand the wave pressure very well. They receive minimal exposure to water; at the most, once a day. They are most often found within cracks and crevices in rocks to minimize their exposure to sunlight, which helps prevent desiccation. Pollicipes polymerus is most commonly found in colonies of many other gooseneck barnacles. They often grow on each other. You can find many smaller goosenecks on the stalk of larger ones. Within the colony the larger goosenecks are found in the center surrounded by the smaller ones in the periphery. They are also very likely to be seen amongst California mussel (Mytilus califonianus) beds (Eckman and Duggins, 1993; Hilgard, 1960; Lane C.C., 2000).

Physical Description

Pollicipes polymerus can be distinguished by its long neck, or stalk. This part of its body is usually 1 inch long. It ranges in color from reddish-brown to brownish-black. The stalk has a leathery appearance with a texture of small bumps. The shell, or capitulum, of P. polymerus grows to be about 2 inches long. It is made up of small plates which enclose its soft body. Inside the shell, the barnacle primarily consists of long segmented legs, intestines, and stomach. The gonads are held within the stalk. The stalk also contains the gland which is used to produce the adhesive that allows barnacles to attach to rocks so well. Pollicipes polymerus can reach up to 8 inches in length (Chase, 1997; Abbott et al., 1980).

Reproduction

Pollicipes polymerus is a hermaphrodite, meaning it is equipped with both male and female reproductive organs. These organs mature at relatively the same rate in the gooseneck barnacles. Although it is hermaphroditic, it usually will not self-fertilize unless there are no other barnacles within about eight inches. It is better for them to cross-breed because it ensures the diversity of their population. Once a female lays eggs, a pheromone is released letting those surrounding males know that she is ready. One barnacle will reach its penis over to a nearby barnacle to release sperm into the shell. Amazingly, it can reach about seven times the animal's diameter. Once the eggs in a neighboring barnacle are fertilized, they are brooded in the mantle cavity. Pollicipes polymerus has a reproductive period of about eight months, and produces about three to four broods (five to seven are possible for a large barnacle.) Thousands of nauplius larvae are then released into the ocean to fend for themselves. These larvae are weak swimmers that spend their time feeding mostly on phytoplankton. Once they reach the cyprid stage they are strong-swimming, non-feeding larvae, with a sole purpose of finding a place to settle. Pollicipes polymerus follow many cues for settlement. Once the cypris larvae have undergone metamorphosis to juvenille barnacles, they will search for a suitable home. They do so by receiving chemical cues from other established barnacles; meaning that there are good conditions. However, this could be a problem when competing for space. They also have to take into consideration the correct temperature, surface texture, and current. All of these factors are crucial for its survival. Gooseneck barnacles are thought to reach maturity at the age of five, and are considered fully grown at the age of twenty (Britannica, 1999-2000; Fox et al., 1997; Hillgard, 1960).

Behavior

The flexible neck of Pollicipes polymerus will readily pull in when touched. This is a form of protection against predators. It can pull in its softer stalk so as to protect it from getting eaten. They also keep their shells closed unless they are eating. This helps prevent desiccation. They can then keep water enclosed inside until water is next accessible. A small limpet, Collisella digitalis, is often found on Pollicipes polymerus' plates. It does not harm the barnacle. (Chase, 1997; Lane C.C., 2000).

Food Habits

Pollicipes polymerus is a filter feeder. Since its head is attached to a usually rocky surface, P. polymerus feeds by extending its legs, or cirri, from its "shell". It separates the valves of its shell and extends the feathery cirri into the water when the tide is in, or when water runs down rocks. Pollicipes polymerus often orients itself to face the current. This explains why, when seen, most are facing the same direction. Pollicipes polymerus will eat a variety of food and is not not selective. Most of its diet consists of small organisms such as plankton, cypris larvae, small clams, hydroids, and amphipods. Food is caught in a lassoing action of the cirri. Six pairs of cirri contract and force the food down towards the mouth parts. Catching the food is aided by many small hairs that line the sides of the segmented cirri. These hairs also aid in the movement of food towards the mouth parts. Since food may be hard to come by at times of low tide, Pollicipes polymerus can use some of its cirri to pass food to the mouth while using others to catch and hold onto new prey when food is abundant. (Britannica.com. Inc., 1999-2000; Chase, 1997; Howard and Scott, Jan-June 1959; Lane Community College, 10/1/00; Wootton, February 1997)

Economic Importance for Humans: Positive

Pollicipes pollicipes is a barnacle that is found in the intertidal of Portugal and Spain. There they are considered a delicacy, and served in gourmet restaurants. Due to local harvesting, their populations become depleted at times. They then seek sources outside of their countries and will then import P. polymerus as a substitute for P. pollicipes, thus bringing in money for the United States (Britannica, 1999-2000).

Conservation Status

Pollicipes polymerus is not endangered, and is abundant along the Pacific coast. The only risk of lowering numbers is if the gooseneck barnacles are overused as a food source for humans (Britannica, 1999-2000).

Other Comments

Gooseneck barnacles are sometimes called such because of their long necks like those of geese. There are many myths that explain the naming of gooseneck barnacles. One of which thought these barnacles to be the source of geese. The myth says that geese grow from these barnacles, which is evident from their growing feathers (cirri) from their shells (Britannica, 1999-2000).

Scientists have also used the name Mitella polymerus for this species (Kozloff 1996)

Contributors

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

native range

the area in which the animal is naturally found, the region in which it is endemic.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.